User`s manual

Version 5.4 497 May 2008
SIP User's Manual 11. Tunneling Applications
11 Tunneling Applications
This section discusses TDM and QISG tunneling, supported by the device.
11.1 TDM Tunneling
The device's TDM Tunneling feature allows you to tunnel groups of digital trunk spans or
timeslots (B-channels) over the IP network. TDM Tunneling utilizes the device's internal
routing (without Proxy control) capabilities to receive voice and data streams from TDM
(E1/T1/J1/) spans or individual timeslots, convert them into packets, and then transmit
them over the IP network (using point-to-point or point-to-multipoint device distributions). A
device opposite it (or several devices when point-to-multipoint distribution is used) converts
the IP packets back into TDM traffic. Each timeslot can be targeted to any other timeslot
within a trunk in the opposite device.
When TDM Tunneling is enabled ('Enable TDM Tunneling' parameter is set to 'Enable' on
the originating device -- refer to ''Configuring the Digital Gateway Parameters'' on page
235), the originating device automatically initiates SIP calls from all enabled B-channels
belonging to the E1/T1/J1 spans that are configured with the protocol type ‘Transparent’
(for ISDN trunks) or ‘Raw CAS’ (for CAS trunks). The called number of each call is the
internal phone number of the B-channel from where the call originates. The 'IP to Trunk
Group Routing' table (refer to ''IP to Trunk Group Routing'' on page 204) is used to define
the destination IP address of the terminating device. The terminating device automatically
answers these calls if its E1/T1 protocol type is set to ‘Transparent’ (ProtocolType = 5) or
‘Raw CAS’ (ProtocolType = 3 for T1 and 9 for E1) and the parameter ChannelSelectMode
is set to 0 (By Phone Number).
Note: It's possible to configure both devices to also operate in symmetric mode. To
do so, set EnableTDMOverIP to 1 and configure the 'Tel to IP Routing' tables
in both devices. In this mode, each device (after it's reset) initiates calls to the
second device. The first call for each B-channel is answered by the second
device.
The device continuously monitors the established connections. If for some reason, one or
more calls are released, the device automatically re-establishes these ‘broken’
connections. In addition, when a failure in a physical trunk or in the IP network occurs, the
device re-establishes the tunneling connections when the network is restored.
Note: It's recommended to use the keep-alive mechanism for each connection, by
activating the ‘session expires’ timeout and using Re-INVITE messages.
By utilizing the ‘Profiles’ mechanism (refer to ''Configuring the Profile Definitions'' on page
212), you can configure the TDM Tunneling feature to choose different settings based on a
timeslot or groups of timeslots. For example, you can use low-bit-rate vocoders to transport
voice and ‘Transparent’ coder to transport data (e.g., for D-channel). You can also use
Profiles to assign ToS (for DiffServ) per source -- a timeslot carrying data or signaling is
assigned a higher priority value than a timeslot carrying voice.